1. Field of the Invention
This invention lies in the field of combustion of waste or dump gases in flare systems. More particularly, it concerns means for preventing the downward movement, beyond a selected point, of atmospheric air into the flare stack system, when the flow of lighter-than-air combusible gases is terminated.
2. Description of the Prior Art
In carrying out some industrial processes, gases, such as hydrogen, light hydrocarbons, and other gases, are often produced. These gases are customarily employed for useful purposes but, on occasion, or as result of some emergency, it is necessary to vent such gases to the atmosphere. These dump, or waste, gases are delivered into the lower portion of a vertically disposed flare stack so that the gases ultimately are released at a significant elevation above the surrounding terrain. Such gases are burned at the upper end of the stack as is well known in the art.
These dump gases are generally lighter-than-air, and have a molecular weight of 28 or less. Many of the gases, upon limited mixture with air, form explosive mixtures. It is, therefore, important to avoid the presence of air below a limited upper portion of the flare stack system to avoid conditions which might promote accidental explosions.
In the prior art it has been customary to inject at the base of the stack a constant, but limited, flow of lighter-than-air purge, or sweep, gases to make sure that there is always flow of gases within the system toward the burning point of the flare, when minor temperature change occurs within the flare. Such additional gas injection is optional, except for major temperature changes in the gas content of the flare. In such cases separate means, such as shown in U.S. Pat. No. 3,741,713, can be adopted to compensate for gas temperature change within the flare system.